In recent years, a high-performance phosphor having high luminous efficiency and brightness and emitting light in a variety of colors has been indispensable for use in a labeling agent in bio-imaging, a display, LED lighting, or the like. In addition, in the display or the lighting, it has been required for a phosphor to have a color rendering property and durability. A conventional phosphor using a rare earth ion or a transition metal ion has been used for a display or the like because of better durability than an organic dye or the like, but does not necessarily have sufficient brightness or color rendering property. A phosphor having higher performance than these phosphors, particularly, a phosphor having high brightness has been demanded.
As a high-performance phosphor to realize these demands, a semiconductor nanoparticle has attracted attention. As a semiconductor nanoparticle to emit fluorescent light, a semiconductor nanoparticle in Group II-VI or Group III-V has been widely known. However, when these semiconductor nanoparticles are used, brightness per particle is not sufficient at present.
On the other hand, in general, brightness of particles formed only of core semiconductor nanoparticles is much lower than semiconductor nanoparticles each having a core/shell structure. By using a semiconductor material having a wider bandgap than a core particle as a shell, a quantum well is formed, and brightness is remarkably improved due to a quantum confinement effect. Therefore, as a method for attaining high brightness, a method for increasing brightness per particle by assembling semiconductor nanoparticles each having a core/shell structure has been considered.
In addition, a technology of confining by dispersing and fixing semiconductor nanoparticles in a matrix such as transparent glass to obtain a solid material exhibiting a high brightness light emission characteristic for a long time under various environments and suitable for an optical application has been also proposed.
Specifically, JP 4403270 B1 and JP 4840823 B1 (corresponding to US 2009/108235 A) disclose a fluorescent glass fine particle having semiconductor nanoparticles dispersed therein by combining a reverse micelle method and a sol-gel method using a precursor of glass. An aggregate using semiconductor nanoparticles and fluorescent enhancement particles together as described in JP 2013-57630 A and an aggregate by controlling aggregation of semiconductor nanoparticles with a physical energy as described in WO 2012/026150 A (corresponding to US 2013/153837 A) have been also known.